System and method to estimate a signal hidden within a composite waveform

ABSTRACT

A system is provided for isolating the value of a signal hidden within a composite electrical signal. The system comprises an input, a processor, and a memory configured to store instructions executable by the processor. The instructions cause the processor to estimate that portion of a received composite electrical signal that represents a hidden signal by subtracting a known first signal from the composite signal.

RELATED APPLICATION DATA

The present application is a divisional application of commonly-ownedand co-pending U.S. patent application Ser. No. 15/194,762 entitledSYSTEM AND METHOD TO ISOLATE AND DISPLAY WAVEFORM COMPONENTS FROM ACOMPOSITE WAVEFORM and filed on Jun. 28, 2016. The present applicationis related to the following commonly-owned U.S. Provisional ApplicationSer. No. 62/186,017, entitled METHOD AND SYSTEM TO ISOLATE AND DISPLAYESTIMATED EKG WAVES and filed Jun. 29, 2015, which application isrelated to and claims the benefit of the following commonly-owned U.S.Provisional Applications: Ser. No. 62/082,297, entitled PHYSIOLOGICALELECTRICAL SIGNAL SIMULATOR and filed on Nov. 15, 2014, and Ser. No.62/111,500, entitled SYSTEM FOR GENERATING CARDIAC WAVEFORMS and filedon Feb. 3, 2015, which applications are incorporated herein by referencein their entireties. The present invention is also related to thefollowing commonly-owned U.S. Pat. No. 9,489,345, entitled SYSTEM ANDMETHOD FOR PROVIDING PRODUCTS AND LOCATIONS, and U.S. Pat. No.10,140,316, entitled SYSTEM AND METHOD FOR SEARCHING, WRITING, EDITING,AND PUBLISHING WAVEFORM SHAPE INFORMATION, which and patents areincorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to an apparatus and method forisolating estimated waveform components from composite waveforms.

BACKGROUND ART

Electrocardiograph (EKG) monitors are important, and non-invasive,diagnostic medical tools. An EKG waveform is a representation of some ofthe electrical activity produced by a beating heart during a period oftime. Two or more electrodes are placed at various location on apatient's skin and connected to an EKG monitor. Electrical signals aregenerated in the heart. The signals are detected on the skin by theelectrodes and received by the EKG monitor. The machine amplifies andprocesses the signals and converts them into a representation of theheart's activity, which may be analyzed and displayed as traces on ascreen, printed onto paper, or both.

It is not the intent of this discussion to provide a detailedexplanation of cardiology and the analysis of EKG traces. However, ageneral summary is useful for background purposes. FIG. 1 is an exampleof a strip chart of electrical signals from a 12-lead EKG monitorconnected to a patient with a normal heart. FIG. 2 identifies individualwaves, intervals, and segments. While there may be some confusion orambiguity about the labeling of different “sections” of an EKG wave, forpurposes of this application an “interval” contains one or moreindividual wave and a “segment” connects the end of one individual wavewith the beginning of the next wave. Beginning from the left side of thechart in FIG. 2, the individual waves are: the P wave, the Q wave, the Rwave, the S wave, the T wave, and the U wave (which may be overlappedand hidden by the T wave and the next P wave).

Beginning again from the left side of the chart in FIG. 2, the intervalsare:

-   -   a. the PR interval, from the start of the P wave to the        beginning of the QRS interval;    -   b. the PQ interval, which if used, is the same as the PR        interval when the Q wave is present;    -   c. the QRS interval (also known as the QRS complex), which        extends from the beginning of the Q wave to the end of the S        wave;    -   d. the ST interval, extends from the end of the S wave to the        beginning of the T wave; and    -   e. the QT interval, is measured from the beginning of the QRS        interval to the end of the T wave; and    -   f. the RR interval, extends from the peak of one R wave of one        beat to the peak of the next R wave of the next beat.

The segments are:

-   -   a. PR segment, extends from the end of the P wave to the        beginning of the Q wave;    -   b. ST segment, extends from the end of the S wave to the        beginning of the T wave; and    -   c. TU segment, extends from the end of the T wave to the        beginning of the U wave.

FIG. 3 identifies the activity of the heart muscles during each of threemajor phases of a beat:

-   -   a. the P wave represents atrial depolarization;    -   b. the QRS interval represents ventricular depolarization; and    -   c. the T wave represents ventricular repolarization.        The wave representing atrial repolarization typically occurs        between the end of the P wave and the beginning of the T wave,        but is typically hidden by ventricular activity.

Many composite waveforms are interpreted or analyzed on the basis ofreceived signals that are conditioned by a variety of processes toenhance the signal before the interpretation process begins. Theconditioning process commonly includes amplification and filtering toremove from the received signal parts of the signal that are believed tonot be useful for the purpose of the interpretation. One example of sucha process is the interpretation of electrocardiograph (EKG) waveformsprovided from EKG machines. An EKG waveform is a representation of someof the electrical activity produced by a beating heart during a periodof time. The signals are detected by electrodes and received by the EKGmachine, which processes the signals and converts them into arepresentation of the heart's activity.

It is not the intent of this discussion to provide a detailedexplanation of cardiology and the analysis of EKG traces. However, itwill be helpful to understand the relationship between PQRST notationand the related cardiac activity of atrial depolarization, atrialrepolarization, ventricular depolarization, and ventricularrepolarization. Generally, the P wave represents atrial depolarization,the QRS complex represents ventricular depolarization, and the T waverepresents ventricular repolarization. Atrial repolarization (Ta wave)occurs during a time period beginning after the P wave and ending aboutthe beginning of the T wave. The Ta is not often identified and isconsidered to be hidden by ventricular depolarization, which usually ismuch larger and occurs during about the same time period. The name Tawave has been given to atrial repolarization activity even though itsonly obvious relation with the T wave seems to be that both representrepolarization. The subscript “a” is used to help avoid confusion withthe T wave. It is known that atrial repolarization may influence anincorrect interpretation of the signal between the QRS complex and the Twave.

The problem of finding a Ta wave in a received EKG is somewhat like asculptor's problem of finding an elephant in a block of stone. A problemreported to have been solved by skilled artists who say they simplyremove everything that doesn't look like an elephant. Of course theproblem of finding a Ta wave is different in at least two ways. On onehand, the problem is more complicated because one doesn't know what thehidden wave looks like, and the removed material must still beexplained.

On the other hand, our material is more forgiving of mistakes and bettersuited to experimentation, analysis, automation, and inventive concepts.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a system for isolating ahidden waveform representing hidden information from a compositewaveform. The system comprises: a processor; a memory configured tostore instructions executable by the processor to cause the processor toestimate that portion of a received composite waveform that represents afirst signal source and generate a waveform that represents an estimatedfirst signal source; and a comparator. The comparator comprises: a firstinput coupled to receive the composite waveform and a second inputcoupled to receive the generated waveform from the processor. Thecomparator is configured to subtract the generated waveform from thecomposite waveform and output a resulting estimated hidden waveform,representing the hidden information.

Other embodiments provide a system for isolating a waveform representingatrial activity from an EKG waveform, comprising: a system inputconfigured to receive an EKG waveform; a processor configured to receivethe EKG waveform from the system input; a comparator having a firstinput coupled to receive the EKG waveform from the system input and asecond input coupled to an output of the processor; and a memoryconfigured to store instructions executable by the processor to causethe processor to: determine that portion of the EKG waveform thatrepresents ventricular activity; and output the waveform that representsthe ventricular activity to the second input of the comparator. Thecomparator is configured to subtract the estimated ventricular activityfrom the full EKG waveform and output the resulting waveform,representing atrial depolarization and estimated atrial repolarization.

Other embodiments provide a system for isolating a waveform representingatrial activity from an EKG waveform, comprising: a system inputconfigured to receive a first waveform that represents an EKG waveform;a processor configured to receive the first waveform from the systeminput; a comparator having a first input coupled to receive the firstwaveform from the system input and a second input coupled to an outputof the processor; and a memory configured to store instructionsexecutable by the processor to cause the processor to: determine asecond waveform that represents estimated ventricular depolarization andoutput the second waveform to the second input of the comparator. Thecomparator is configured to subtract the second waveform from the firstwaveform and output a third waveform, the third waveform representingatrial depolarization and estimated atrial repolarization.

Another embodiment provides a method of estimating hidden information ina composite waveform

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an prior art example of a strip chart of electrical signalsfrom a 12-lead EKG monitor connected to a patient with a normal heart;

FIG. 2 is a prior art representative plot that identifies the individualwaves, intervals and segments that combine to form an EKG wave;

FIG. 3 is a prior art representative plot that identifies the activityof the heart muscles during each phase of a beat;

FIG. 4 illustrates an exemplary EKG waveform with transition breakpoints identified;

FIG. 5 illustrates a TABLE that may be used to enter information tospecify the location of break points when constructing a representationof a heart beat waveform;

FIG. 6 illustrates another TABLE that may be used to enter informationto specify the location of break points when constructing arepresentation of a heart beat waveform;

FIG. 7 illustrates another TABLE that may be used to enter informationto specify the location of break points when constructing arepresentation of a heart beat waveform;

FIG. 8 illustrates still another TABLE that may be used to enterinformation to specify the location of break points when constructing arepresentation of a heart beat waveform;

FIGS. 9A and 9B illustrate a screen shot of a display, including a tablewith drop-down selections and a representation of an EKG waveformconstructed from the selections;

FIG. 10 is a block diagram of an embodiment of a EKG simulator of thepresent invention;

FIG. 11 is a block diagram of an embodiment of a detector of the presentinvention;

FIG. 12 illustrates a screen shot of a display of the construction of anEKG waveform generated by summing representations of an atrialdepolarization wave, an estimated atrial repolarization wave, aventricular depolarization wave, and a ventricular repolarization wave;and

FIG. 13 is a flowchart of an embodiment of a method of using the systemof FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are provided toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components and so forth. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

FIG. 4 illustrates an exemplary EKG waveform showing two beats B₁ and B₂with break points B₁M₁-B₁M₁₅ and B₂M₁-B₂M₁₅, respectively. The breakpoints M₁-M₁₈ identify fiducial or transition points of one completecycle of an EKG waveform.

(Any wave, interval, or segment will be referred to generically hereinas a “section.”) TABLE I provides an identification of the break pointsas used in this description. Although these identifiers may differ fromconventional designations, they will be used in this description.

TABLE I Break Point Identifier M₁ Beginning of beat M₂ Beginning of Pwave (P₁) M₃ Peak of P wave (P₂) M₄ End of P wave (P₃); beginning ofPQ/PR interval M₅ Beginning of Q wave (Q₁) M₆ Low point of Q wave (Q₂)M₇ End of Q wave (Q₃); beginning of R wave (R₁) M₈ Peak of R wave (R₂)M₉ End of R wave (R₃); beginning of S wave (S₁) M₁₀ Low point of S wave(S₂) M₁₁ End of S wave (S₃); beginning of ST interval M₁₂ End of STinterval; beginning of T wave (T₁) M₁₃ Peak of T wave (T₂) M₁₄ End of Twave (T₃) M₁₅ Beginning of U wave (U₁) M₁₆ Peak of U wave (U₂) M₁₇ Endof U wave (U₃) M₁₈ End of beat

For example, the sequence M₂-M₄ identifies the P wave while the sequenceM₅-M₁₁ identifies the QRS complex. Each break point may be definedrelative to the previous break point. Thus, an x-value would designatethe difference in time (width) from one point to the next and a y-valuewould designate the positive or negative difference in amplitude.Alternatively, each point may be defined by its absolute x-y coordinatesrepresenting time and amplitude, respectively, referenced to the y- andx-axis, respectively.

Either or both of the x and y parameters of a break point may eitherindicate their absolute values, that is their distance from the y-axisor x-axis, respectively, or may indicate their distance along theirrespective axis from the previous break point, that is the “delta.” Asused herein, the term “value” will refer to a delta and the term“coordinate” will refer to an absolute value. However, preferably the xparameter of a break point will be indicated by the x-value (its deltafrom the previous break point) and the y parameter will be indicated bythe y-coordinate (its absolute value from the x-axis).

In order to define a section, it is also necessary to define a path fromone break point to the next. The path is identified by an interpolationmethod i. Some examples of interpolation methods include, but are notlimited to, straight line, sinusoidal, square, concave upward, concavedownward, notched, among others.

Thus, each break point may be assigned three parameter values x, y, iwhich together define the location of a break point and the path fromthe break point to the next break point.

A tools may be provided to allow a user to build a waveform from asequence of sections. For example, after logging into a web service, auser may be presented with a series of pages, each illustrating aparticular section with a selection of varying shapes and widths (intime). For example, one page may allow a user to select a PQ interval bypresenting a one-column, nine row table with the rows showing possiblePQ intervals from 120 ms to 200 ms in increments of 10 ms. Another pagemay allow a user to select the overall RR interval by presenting aone-column, seven-row table with the rows showing possible RR intervalsfrom 0.6 l to 1.2 sec. in 0.1 sec. increments. A user may thus makedesired selections and construct one or more full heartbeat waveforms.The assembled waveform may then be output as a data file to be loadedinto an EKG simulator for research, teaching, testing, and trainingpurposes.

As an alternative to the page-by-page entry method, a user may bepresented with a substantially empty table to be filled in with x-valuesfor the break points; that is, time differences from earlier breakpoints. FIG. 5 is an example of a table that may be displayed to theuser. The first column and first row identify the break points using thesame identification numbers as are used in FIG. 4, M₁-M₁₈. The secondcolumn and second row identify each break point by reference to thewave, interval, or segment in which the break point is located (seeTABLE II above). The user may enter a value into each blank cell todesignate a time difference between one break point and another. In thetable, several cells have been filled in for clarity. For example, todefine the total width of the P wave, a value for the time P₃-P₁ wouldbe entered into the cell at the intersection of column M₄ for breakpoint P₃ with row M₂ for break point P₁. Similarly, to define the totalwidth S₃-Q₁ of the QRS complex, a time value would be entered into thecell at the intersection of column M₁₁ for break point S₃ with row M₅for break point Q₃. The user may fill in as many other cells as desiredto specify other time differences. As will be appreciated, the cells atthe intersection of break points with themselves have a zero value andthe cells that represent negative distances to a previous break pointmay contain negative values or left blank. In addition, the cells in therow of M₁ are unassigned. FIGS. 9A and 9B illustrate completed table 906and the resulting waveform 910 generated by the values entered into thetable cells of rows/columns R2-R16/C5-C19.

An alternative simplified table, illustrated in FIG. 6, may be displayedfor the user to enter the x-coordinate (the distance from the y-axis) ofeach break point, M₁-M₁₈. It will be understood that the break pointlabels M₁-M₁₈ and P₁-U₃ used in the tables of FIGS. 6-8 are the samelabels as are used in the tables of FIGS. 4 and 5. After the user hasentered coordinates into each cell and has optionally overridden anydefault coordinates, the user may change any entry by re-entering acoordinate into a cell. However, the user may be prevented frominputting an invalid entry, such as a coordinate that is less than thecoordinate of the preceding break point or greater than the coordinateof the next break point.

Another table, shown in FIG. 7, may be displayed for the user to enterthe amplitude of each break point, M₁-M₁₈. Optionally, a default valuemay be associated with some or all of the break points. For example, asillustrated in FIG. 7, the break points that identify the beginning andend of sections of a beat may default to an isoelectric line whileleaving the break points that identify peaks and valleys of waves to befilled in by the user. The user may override any default amplitude valueby replacing it with a desired value.

Further, another table, illustrated in FIG. 8, may be displayed for theuser to enter the interpolation method for the path from each breakpoint to the next. Again, certain paths may be assigned a default path.For example, the path from M₄/P₃ to M₅/Q₁ (the PQ segment) may defaultto a zero-slope straight line. The path from M₇/R₁ to M₈/R₂ (the firstpart of the R wave) may default to a straight line whose slope willdepend on the amplitude of M₈/R₂. And, the path from M₁₂/T₁ to M₁₃/T₂(the first part of the T wave) may default to a partial sinusoidal shapewhose exact characteristics will depend on the amplitude of the breakpoint M₁₃/T₂. As with the amplitude entries, the user may override anydefault path interpolation method by replacing it with a desired method.

Although in some versions the user may enter coordinates and values in afree-form fashion, in other versions the user may be presented with adrop-down list of suggested and valid coordinates or values from whichto select.

The tables of FIGS. 7 and 8 are illustrated as separate tables forclarity. In practice, either or both tables may be integrated into thetable of FIG. 5 as additional columns and displayed to the user as asingle table.

An interactive matrix control/display such as shown in FIGS. 9A and 9Bmay have many features that help users learn about their measurement andmonitoring tools at the same time they enhance their own skills in usingand evaluating these tools. The waveform display 910 is scaled using theFSx control 902 and the FSy control 904. The waveform shape is definedby a shape value directly under the waveform display 910. The textstring represents the shape value in an x,y,i format. When using thecontrol/display it is not necessary to know how to interpret the shapevalue, but it is helpful to understand that the displayed waveform isdefined by and may be generated from either the shape value or from theshape data in the matrix. In other words, given the shape value, thesystem can generate the waveform and populate the matrix with data. Viceversa, given the matrix data the system can generate the waveform andthe shape value. The matrix contains more data than the shape value, butall the matrix shape data can be derived from the shape value. Togenerate the waveform, the system needs x,y, and i data for eachbreakpoint, 14 in this case. If three independent break points weredefined for each of the six fiducial points (PQRSTU), 18 points would berequired, but in this case fiducial points Q2/Q3/R1 share one point andR3/S1/S2 share one point. So only fourteen breakpoints are required foreighteen fiducial points. Sixteen break points are identified for thewaveform shown in FIG. 4 because Q2 and S2 each have their own breakpoint leaving only Q3/R1 to share one point and R3/S1 to share another.

FIGS. 9A and 9B illustrate a screen shot of an interactivecontrol/display 900 that may be presented to a user to construct an EKGor other waveform. Using a touch screen, mouse, or other input device,the user may select a range of values for the x-axis 902 and for they-axis 904. The lower portion of the display 900 presents a matrix 906of one variation of the table of FIG. 5 with elements of FIGS. 7 and 8and other features integrated into it. The first row R1 and first columnC1 identify the three break points of each wave P, Q, R, S, T, and U.Because some break points corresponding to fiducial points typicallycoincide with other break points with no change in x and y coordinates,they are not shown separately. The cells in the second column C2 allowthe user to select an interpolation method i, such as from a list oricon display 908. The cells in the third and fourth columns C3, C4 allowthe user to select, such as from drop-down lists, the absolute amplitude(along the y-axis) and the absolute time (along the x-axis),respectively, of each break point. The cells at the intersections of theremainder of the rows R2-R16 and columns C4-C18 provide drop-down liststhat allow the user to select values that represent the timedifferential between the break point identified in column C1 and thebreak point identified in row R1. Cells at the intersection of breakpoints with themselves represent a zero distance and may be left blankor contain symbols such as dashes that are believed to be more usefulthan zeros. Negative values are shown in the lower half of the matrix.Thus, for each break point, the user may either enter an x-coordinate(the absolute time along the x-axis) in column C2 or enter an x-value(difference from the previous break point) in an appropriate cell in themain body of the matrix 906.

In addition, the user may select an interpolation method from a set oficons 908 to define a path from one break point to the next, andpreferably a column C2 may be inserted to identify the iValue selectedfor each break point.

Displayed between the x, y, and i selections 902, 904, 908 and thematrix 906 is a complete graphical representation of a waveform, in thiscase a heart beat, from the first break point to the last. Thus, theuser is able to see the creation of the waveform progress as entries areinput into the cells of the matrix. The user is further able to changeany entry in real time and immediately see the effect on the chart. Inone embodiment (not shown), the break points displayed in the waveformrepresentation are aligned with their respective columns in the matrixbelow.

The display of the waveform representation may be interactive wherebythe user may use an input device to “grab” and move break points to newlocations in the x or y directions directly on the chart.

After the user has entered desired information, the waveform may beassembled digitally and then output as a data file. The data file may beloaded into an EKG simulator to simulate a patient's heart for testingor training purposes.

FIG. 10 is a block diagram of an embodiment of a signal simulator 100 ofthe present invention. The simulator 100 is coupled to the control anddisplay panel 900 and is configured to output signals to a system undertest (SUT) 10, such as an EKG or other biological signal monitor. Thepanel 900 and simulator 100 may be coupled through a wired connectionor, preferably, through a wireless connection, such as WiFi orBluetooth® enabled. In such a configuration, the panel 900 may thus beused remotely.

The simulator 100 may include a communication (comm) port 102 configuredto receive programming signals from the panel 900, a memory 104configured to store instructions and predetermined values, a processor106 configured to process the programming and predetermined valuesaccording to the instructions stored in the memory, a digital-to-analogconverter (DAC) 108 configured to convert the processed values intoanalog output signals, and an output port 110 configured to make theanalog output signals available to the SUT 10. The simulator 100 mayalso include an input port 112 to receive signals from the SUT 10 and acomparator 114 configured to compare the signals 114A from the SUT 10against the signals 114B from the DAC 108. A comparison of the signals,such as in graphical form, may then be displayed on the panel 900.Although the input port 112 and the comparator 114 are shown in FIG. 10as being digital components, they may instead be analog components, inwhich case the input signals 114B would be received directly from theprocessor 106 without conversion.

The panel 900 may be part of any appropriate input and display product,such as a computer, tablet computer, or smart phone, to receiveprogramming values from a user, output programming signals to thesimulator 100, and receive signals for display from the simulator 100.

The simulator 100 may transmit simulated physiological electrical(biological process) signals to the monitor SUT 10 in place of signalsfrom patient electrodes for the purpose of testing or verifying variousfunctions of the monitor. When the SUT 10 is an EKG monitor, suchfunctions may include those related to variations in heart rate. Asnoted above, the comparator 114 is configured to compare the signalsfrom the SUT 10 against the signals from the DAC 108 and a comparison ofthe signals may then be displayed on the panel 900. In this manner, theperformance of the SUT 10 may be verified and adjustments may be made asrequired, such as if the two signals are misaligned.

The simulator 100 may also be programmed to identify when thedifferential between two break points falls outside of a predeterminedrange, thus indicating the possibility of an abnormality. For example,when the simulator 100 is coupled to an EKG monitor (SUT 10), it maymeasure the time between the T₃ break point to the next R₂ break point.If time is less than about 260 ms, a heart irregularity may be indicatedand the simulator 100 may provide an appropriate warning signal to theuser.

The raw signal that is received by an EKG monitor is not “pure” in thatthe electrodes also pick up unrelated electrical activity, circuitrynoise, and other artifacts, all collectively referred to herein asnoise. An EKG monitor includes circuitry to filter out the noise so thatthe wave form that is displayed is relatively clean. The simulator 100may also include a noise generator 116 and be programmed to inject ormix noise into a user-created EKG wave form to more accurately simulatethe signals from an actual patient's heart. The mixed signal istransmitted to the monitor or SUT 10 through the output port 110, fedback to the simulator 100 through the input port 112, and compared 114to the transmitted signal. In this manner, the capability of the monitoror SUT 10 to filter the noise and leave only the useful information maybe assessed.

The simulator 100 may provide an additional training benefit by allowingusers to generate custom designed EKG waveforms for study, instead ofhaving to find and study actual EKG patient charts that may be unclear,inconsistent, noisy, or contain various artifacts.

An embodiment of the present invention includes a method and system toisolate and display the Ta wave, which represents atrial repolarizationand which is typically not visible on an EKG. FIG. 11 is a block diagramof an embodiment of such a detector 200. The detector 200 includes acomm port 202 through which the control panel and display 900 maycommunicate with the detector 200. The detector 200 also includes amemory 204 configured to store instructions and a processor 206configured to process the programming according to the instructionsstored in the memory 204 The detector 200 also includes an input port208 configured to receive analog signals from an EKG monitor and ananalog-to-digital converter (ADC) 210 configured to convert the receivedsignals into digital signals to make the digital signals available tothe processor 206. It will be appreciated that the EKG monitor 20 mayhave a digital output in which case the ADC 210 is unnecessary and thesignal from the input port 208 may be sent directly to the processor206.

Instructions stored in the memory 204 and executed by the processor 206cause the processor 206 to receive a full EKG waveform from the EKGmonitor and estimate the portion of the EKG waveform that representsventricular depolarization and repolarization. Further instructionscause the processor 206 to send the estimated ventricular waveforms asone input to a comparator 212. A second input to the comparator 212receives the full EKG from the ADC 210 (or directly from the input port208). The comparator 212 subtracts the estimated ventricular waveformsfrom the full EKG waveform and outputs the result to an output port 214for display or printing and analysis. The output result representsatrial depolarization (PR Interval) and estimated atrial repolarization(Ta wave).

Determination of estimated ventricular depolarization may be made in anumber of ways. The processor may be programmed to identify theappropriate break points. Referring to TABLE II above and FIG. 4, thesebreak points include: Q₁(M₅), Q₂(M₆), Q₃/R₁(M₇), R₂(M₈), R₃/S₁(M₉),S₂(M₁₀), S₃(M₁₁), T₁(M₁₂),T₂(M₁₃), and T₃(M₁₄). Alternatively, a user ofthe system 200 may manually enter the breakpoints through the controlpanel and display 900 as described above.

It is believed that the estimated ventricular depolarization may also bedetermined through frequency or Fourier analysis. The inventor believesthat ventricular depolarization results in electrical signals that areat a higher frequency than electrical signals from atrialrepolarization. Consequently, the processor 206 may be programmed withinstructions to send to the comparator 212 that portion of the selectedselection of the EKG signal having frequency components above apredetermined level, representing ventricular depolarization. After thecomparator 212 subtracts this portion of the full EKG signal, the outputresult represents an estimated representation of the atrialrepolarization. Alternatively, the processor 206 may be programmed withinstructions to determine that portion of the full EKG signal having afrequency below a predetermined level and directly output arepresentation of atrial activity.

The inventor also believes that the Q and S waves may be affected by theTa wave. Thus, in another embodiment, instructions stored in the memory204 and executed by the processor 206 again cause the processor 206 toreceive a full EKG waveform and to estimate ventricular depolarization.Further instructions cause the processor 206 to send the estimated waveas one input to the comparator 212. A second input to the comparator 212receives the full EKG from the ADC 210 (or directly from the input port208). The comparator 212 subtracts the estimated wave from the full EKGwaveform and outputs the result to the output port 214 for display orprinting and analysis. The output result may then represent an EKGwaveform with estimated atrial repolarization instead of a compositesignal including both atrial and ventricular activity.

As with the previous embodiment, determination of ventriculardepolarization may be made in a number of ways, including programmingthe processor with the appropriate break points (R₁(M₇), R₂(M₈), andR₃(M₉)) or entering the break points manually. An example of suchprogramming is illustrated in FIG. 12, which is a screen shot of adisplay of the construction of an EKG waveform. The full waveform, shownin the bottom plot, is generated by summing representations of an atrialdepolarization wave (top plot), an estimated atrial repolarization wave(second plot), a ventricular depolarization wave (third plot), and aventricular repolarization wave (fourth plot).

Sources for information used to estimate repolarization anddepolarization for atrial and ventricular activity include thefollowing: EKG Data Bases, various electrode lead configurations,frequency content of portions of fiducial waveforms, expert opinions,intra-cardiac and catheter electrodes, missing beats, what-if scenarios,trial and error comparisons, comparison of normal beats with otherwisenormal without atrial activity, otherwise normal beats withoutventricular activity, statistical methods including Bayes conditionalprobability techniques to improve estimates based on prior estimates,methods used for identifying musical instruments, and other sources ofsound and electrical activity.

With respect to a method of estimating hidden information or wave in acomposite waveform, the section of a waveform in which the hidden waveis expected to be found (search section SS) is identified by defining astart point and a stop point on the x-axis. The SS wave may include manycomponents, but for simplicity just two components are relevant: adominant wave P1 and a hidden wave P2. Any other components that may bein the composite wave are treated as not being significant for purposesof estimating the hidden wave. These other components are assumed to beincluded in either P1, P2, or overlapping both. When defining P1, theintent is to define a wave that is less complex than SS but stillbelieved to not affect the analysis leading to an interpretation orreading of the composite waveform.

For example, a reading of an EKG generally indicates whether thewaveform is normal or not normal with clarifying additional remarks andcommonly d'esn't consider atrial repolarization (the Ta wave or repA).When trying to isolate a wave that represents the usually hidden waverepA, a plausible section SS of the full EKG waveform in which to searchwould contain waves believed to include the hidden wave and ventriculardepolarization (the QRS complex or depV). In this case, the SS is thecomposite wave which has two components, repA and depV. A simplifiedversion of the dominant wave depV is defined as P1 with theunderstanding that SS=P1+P2. P2 may then be calculated as P2=-SS −P1.For an EKG, reading this corresponds to repA =-SS −depV, where P1=depVand P2=repA. Now a decision is made about whether depV has been definedin a way to provide an SS that is a plausible representation of thewaveform used by the analysis process to provide the reading. Whenadding or subtracting component parts of a composite waveform, it isassumed that each component has the same number of samples as thecomposite waveform as illustrated in FIG. 12. For simplicity, it alsohelps to consider that the isoelectric line has zero amplitude and thatsample amplitudes have positive and negative amplitudes around it.

More specifically referring to the flowchart of FIG. 13, an embodimentof a step by step method of using the system is as follows:

-   -   300. Begin.    -   302. Set n=1.    -   304. Receive a composite wave signal with an interpretation        called Reading(n) that describes support and diagnosis without        performing an isolation process.    -   306. Define a Search Section (SS) within the composite signal        that includes a waveform having characteristics believed to be        essential based on current conditions to support the reading.    -   308. Define Part 1 (P1) of SS where P1 is estimated to be        substantially less complicated than SS but still supports the        Reading.    -   310. Set Part 2 (P2)=SS−P1.    -   312. If P2 is not plausible, go to Step 326, otherwise continue.    -   314. Set SS=P1.    -   316. Set n=n+1.    -   318. Receive Reading (n).    -   320. If Reading(n) equals Reading(1), P2 has no significant        effect on Reading(1) and go to Step 334, otherwise continue.    -   322. P2 changes Reading(n).    -   324. Decide on further action and go to Step 334.    -   326. Adjust P2.    -   328. Set P1=SS−P2.    -   330. If P1 is plausible, go to Step 314, otherwise continue.    -   332. If SS is plausible, go to Step 308, otherwise go to Step        306.    -   334. End.

This step by step method is an iterative process that may help usersdecide whether waveform isolation helps improve their interpretationsand to collect data for future applications.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A system for estimating a signal hidden within acomposite electrical signal, the system comprising: an input forreceiving an electrical signal and a first reading, the electricalsignal comprising a search section SS comprising the sum of a firstsignal P1 and a hidden second signal P2 and the first reading describingan initial evaluation of the electrical signal based upon an assumptionthat SS equals P1 without regard to the hidden signal P2; a processorcoupled to the input; and a memory configured to store instructionsexecutable by the processor to cause the processor to: estimate thehidden signal P2; and calculate a new signal P1 from which a secondreading is provided, the second reading describing an updated evaluationof the electrical signal based upon subtracting the estimated hiddensignal P2 from the search section SS; whereby, if the second reading isdifferent from the first reading, the effect of the estimated hiddensignal P2 is considered before taking action based on the first andsecond readings.
 2. The system of claim 1, wherein: the compositeelectrical signal is an EKG signal; the first signal P1 comprises aportion of the EKG signal representing a ventricular depolarization wavedepV; the hidden signal P2 comprises a portion of the EKG signalrepresenting an atrial repolarization wave repA; and the search sectionSS comprises a section of the EKG signal believed to include theventricular depolarization wave depV and the atrial repolarization waverepA; whereby, the processor estimates depV and repA from the relationsSS=depV+repA.
 3. The system of claim 1, comprising further instructionscausing the processor to determine whether the signals P1 and P2 areplausible.
 4. The system of claim 3, comprising further instructionscausing the processor to alternately change signal P1 and signal P2until both are plausible based on SS=P1+P2.
 5. The system of claim 3,comprising further instructions causing the processor to determinewhether the search section SS is plausible.
 6. A method for estimating asignal hidden within a composite electrical signal, the methodcomprising: receiving a composite electrical signal and a first reading,the composite electrical signal comprising a search section SScomprising the sum of a first signal P1 and a hidden second signal P2and the first reading describing an initial evaluation of the compositeelectrical signal based upon an assumption that SS equals P1 withoutregard to the hidden signal P2; and estimating the hidden signal P2;calculating a new signal P1 from which a second reading is provided, thesecond reading describing an updated evaluation of the compositeelectrical signal based upon subtracting the estimated hidden signal P2from the search section SS; and if the second reading is different fromthe first reading, considering the effect of the estimated hidden signalP2 before taking action based on the first and second readings.
 7. Themethod of claim 6, wherein: the composite electrical signal is an EKGsignal; the first signal P1 comprises a portion of the EKG signalrepresenting a ventricular depolarization wave depV; the hidden signalP2 comprises a portion of the EKG signal representing an atrialrepolarization wave repA; and the search section SS comprises a sectionof the EKG signal believed to include the ventricular depolarizationwave depV and the atrial repolarization wave repA; and estimating depVand repA from the relation SS=depV+repA.
 8. The method of claim 6,further comprising determining whether the signals P1 and P2 areplausible.
 9. The method of claim 8, further comprising alternatelychanging signals P1 and P2 until both are plausible based on SS=P1+P2.10. The method of claim 8, further comprising determining whether thesearch section SS is plausible.